1. Field of the Invention
The invention relates to an actuator or servo device comprising an actuator member adapted to move linearly in the motion space of an actuator housing, a microwave position detecting device for detecting the position of the actuator member in the motion space, the actuator member producing a pressure wave acting on the position detecting device on approaching the position detecting device and a high frequency microwave antenna arrangement for emitting and receiving microwaves, which are at least partially reflected by the actuator member.
2. Description of the Related Art
Such an actuator is for example described in the German patent publication DE 102 05 904 A1. In this case an actuator device in the form of a pneumatic cylinder with an actuator member is described which is constituted by a piston of the cylinder. The position detecting device comprises a high frequency microwave antenna arrangement for detecting the clearance or, respectively, the position of the piston from an annular abutment, which surrounds the microwave antenna arrangement annularly. On drawing close to the microwave antenna arrangement the piston causes a pressure wave in front of it, which mechanically loads the microwave antenna arrangement and thus for example changes the . position of the microwave antenna arrangement in relation to the housing. Accordingly the clearance measurement signal, which is produced by the position detecting device, is influenced comparatively strongly. Furthermore the measurement-related signal may fail.